1. Field of the Invention
This invention relates to a fire retardant thermosetting resin composition containing tricalcium aluminate hexahydrate as a filler which renders the thermosetting resin composition fire retardant.
2. Description of the Prior Art
It is extremely important to render resins used in construction materials fire retardant from the viewpoint of fire prevention and protection of human life, and such fire retardant resins have also been greatly needed in the fields pf packing materials, furniture, toys, electric utensils and transport vehicles. Many prior art studies and inventions concerning such fire retardant resins have been made, but recently improvements therein have been earnestly needed.
It is known that the addition of antimony trioxide is effective for rendering plastics or rubber fire retardant, and antimony trioxide has often been used for this purpose by incorporation with halogenated resins together with clay. However, the use of antimony trioxide has not been satisfactory because of the high cost and toxicity thereof, and in addition, sufficient fire retardancy has not been obtained. In order to overcome these defects, inorganic fillers containing water of crystallization have been recently utilized, which dehydrate in the vicinity of the decomposition temperature of plastics to control temperature elevation and to accelerate carbonization.
Research has clarified the compatibility of aluminum hydroxide with plastic materials, and C-331 and Hydral 710 (trade names of the Allied Chemical Corporation have been used for this purpose as has been reported by W. J. Connolly and A. M. Thornten, 20Th SPI Sec. 11B(1965). Other used aluminum hydroxides include Higilite (trade name) which is sold commercially by Showa Denko K.K. in Japan. Particles of this aluminum hydroxide are shaped in hexagonal plate form, they contain 35% by weight of water of crystallization, and the dehydration temperature thereof is about 200.degree. to 300.degree.C.
The following citations describe some of the representative related prior art inventions: Japanese Patent Publication No. 263/70 discloses the use of a mixture of aluminum hydroxide and an organic halide, Japanese Patent Publication No. 3962/68 teaches the addition of an inorganic filler containing chemically bound water to an ester containing polymer, and Japanese Patent Publication No. 10535/72 also teaches the addition of an inorganic filler to an epoxy resin. In addition for the purpose of improving the tracking resistance of insulators magnesium hydroxide has been added to thermosetting resins (Japanese Patent Publication No. 16236/63), and lithium hydroxide has been added to vinyl chloride (Japanese Patent Publication No. 25766/67). Japanese Patent Publication No. 22577/71 discloses the incorporation of an adsorbent containing adsorbed water in thermoplastic high molecular weight substances thereby to impart self fire extinguishability thereto, which, however, is questionable in view of the fact that the composition explodes during treatment thereof.
The effectiveness of zinc borate, 2ZnO.3B.sub.2 O.sub.3 .3.5H.sub.2 O, for rendering halogenated polyesters and vinyl chloride fire resistant is disclosed in Japanese Patent Publication No. 13149/71 and in W. G. Woods and J. G. Bower, 25th SPI Sec. 9B (1970). The dehydration temperature of the zinc compound is suitably 250.degree.C, but the water content thereof is relatively small (15% or less), and in addition, this compound is very expensive.
On the other hand, it is known that about 50 to 60% by weight of water can be dispersed in unsaturated polyesters in the form of a water-in-oil dispersion, and this is effective for rendering this polymer fire retardant. However, this technique is defective in that the polymer gradually drys and contracts, and therefore, it is particularly difficult to utilize this polymer for external construction members from the viewpoint of the poor water-proof character thereof. For the purpose of stabilizing the water content in such a polymer, another method is suggested wherein calcined gypsum, calcium sulfoaluminate, tricalcium aluminate and gypsum, or calcium sulfoaluminate and Portland cement is (are) added, in addition to water, to form hydrates as disclosed in Japanese Patent Publication Nos. 11808/71, 10807/71, 22723/71 and 22726/71. In this method, the reaction product is gypsum dihydrate or ettringite (3CaO.Al.sub.2 O.sub.3 .33CaSO.sub.4.32H.sub.2 O), and these products are alkaline. Accordingly, some products exist in this method in that the alkaline substances inhibit the hardening of resins and in that dehydration tends to occur due to heat of polymerization and hydration.
A method has been recently developed in which calcium sulfite which is obtained in desulfurization of exhaust fumes is combined with thermoplastic resins such as polyethylene as disclosed in Japanese Patent Publication No. 38333/71. Particles of calcium sulfite are nearly spherical, and they have the advantage that (1) many particles can be combined with these resins and (2) the dehydration temperature thereof is relatively high. On the other hand, however, the water content thereof is small, and thus it is difficult to attain resins which have been rendered sufficiently fire retardant in character. Rather, resins with calcium sulfite can be burned to a moderate extent.
As described above, various attempts have been made for the purpose of rendering plastics fire retardant, particularly thermosetting resin compositions, but additional improvements in fire retardant resins have been recently needed. In view of this need, systematic studies and investigations have been made on fire retardant resins and the present invention has been thus discovered. As a result of research the following facts have been found: Addition of a large amount of fire retardant fillers decreases the needed amount of resin, which is in many cases economically advantageous. However, it is necessary to select fillers whose particles are nearly spherical so that the shapability and mechanical properties of compositions are not be degraded. In addition, preferred fillers contain bound water which are dehydrated when heated to the vicinity of the decomposition temperature of resins thereby to control temperature increase, and further, the generated water vapor should cut off air to prevent flaming and to accelerate carbonization. The present invention is one in which this preferred phenomenon is achieved, and after systematic investigation of various kinds of inorganic fillers of hydroxides, salt hydrates, aluminate hydrates, silicate hydrates and carbonates, and it has been found that a thermosetting resin composition containing tricalcium aluminate hexahydrate 3CaO.Al.sub.2 O.sub.3 .6H.sub.2 O (hereinafter referred to as C.sub.3 AH.sub.6) is fire retardant.
Salt hydrates include Na.sub.2 SO.sub.4 .10H.sub.2 O which contain an extremely large amount of bound water. This hydrate, however, is defective in that the dehydration temperature thereof is low and therefore easily dehydrates during kneading, resulting in difficulty in the manufacture of shaped articles, or otherwise, also easily dehydrates during use, resulting in a degradation of the weatherproof property of the resins. In addition, this hydrate has a high solubility, which also deteriorates the water-proof property of the resins.
Calcium aluminate hydrates and calcium sulfoaluminate hydrates have analogous defects. Of the calcium aluminate hydrates, CaO.Al.sub.2 O.sub.3 .10H.sub.2 O is relatively preferred, and the dehydration temperature thereof is about 190.degree. to 300.degree.C, which is quite desirable. However, this hydrate tends to change to C.sub.3 AH.sub.6 over the course of a long period of time. Of the calcium sulfoaluminate hydrates, 3CaO.Al.sub.2 O.CaSO.sub.4 .18H.sub.2 O loses a half of the bound water therein at 100.degree.C, and 3CaO.Al.sub.2 O.sub.3 .3CaSO.sub.4 .32H.sub.2 O loses two thirds of the bound water therein at 100.degree.C. Since 3CaO.Al.sub.2 O.sub.3 .3CaSO.sub.4 .32H.sub.2 O is needle-shaped, a large amount of these needles is difficult to combine with resins.
On the other hand, some carbonates have bound water therein whose decomposition heat absorption is large, but they have high decomposition completion temperature and most of them can not be very efficiently used to render resins fire retardant. For example, dehydration of MgCO.sub.3 .3H.sub.2 O occurs at about 30.degree. to 250.degree. C and decarboxylation thereof at about 400.degree. to 500.degree.C. Thus, this carbonate moderately decomposes over a broad temperature range.